A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded to a circuit layer made of a conductive material.
A power semiconductor element for controlling higher amounts of power used to control wind power generation, electric automobiles, hybrid automobiles, and the like generates a large amount of heat. Therefore, as a substrate on which such a power semiconductor element is mounted, for example, a power module substrate including a ceramic substrate made of AlN (aluminum nitride), Al2O3 (alumina), and the like, and a circuit layer formed by bonding a metal plate having excellent conductivity to one surface of the ceramic substrate has been widely used until now. As the power module substrate, a substrate having a metal layer formed by bonding a metal plate to the other surface of the ceramic substrate is also provided.
For example, PTL 1 proposes a power module substrate in which a first metal plate and a second metal plate which constitute a circuit layer and a metal layer are copper plates, and these copper plates are directly bonded to a ceramic substrate using a DBC method. In the DBC method, by utilizing a eutectic reaction between copper and a copper oxide, a liquid phase is formed at the interface between the copper plate and the ceramic substrate to bond the copper plate to the ceramic substrate.
Further, PTL 2 proposes a power module substrate in which a circuit layer and a metal layer are formed by bonding copper plates to one surface and the other surface of a ceramic substrate. In the power module substrate, the copper plates are bonded to the ceramic substrate by performing a heating treatment in a state in which the copper plates are arranged on one surface and the other surface of the ceramic substrate via a Ag—Cu—Ti-based brazing filler metal (a so-called active metal brazing method). In the active metal brazing method, since a brazing filler metal containing Ti which is an active metal is used, the wettability between the melted brazing filler metal and the ceramic substrate is improved and the ceramic substrate and the copper plates are bonded in a satisfactory manner.